1. Field of the Invention
The present invention relates to a spot welding system and a robot used for the spot welding system.
2. Description of the Related Art
Execution of spot welding causes deformation or abrasion of an electrode of a welding gun, or adhesion of an oxide film to a surface of the electrode. For this reason, a polishing step (dressing) of polishing the electrode surface is carried out periodically. Dressing changes a tip position of the electrode, so that the tip position of the electrode needs to be detected again.
JP-A-2000-176649 discloses an electrode abrasion correction method for correcting an electrode abrasion amount in a spot welding gun of a robot. In the electrode abrasion correction method, an amount of electrode abrasion is calculated at the time of electrode chip replacement and during cycle operation in different manners. In JP-A-2000-176649, particularly, during cycle operation, abrasion amounts of a movable electrode and a fixed electrode are distributed according to a predetermined ratio obtained through a test in advance, so as to more accurately estimate the abrasion amounts.
However, although the technique disclosed in JP-A-2000-176649 reduces the time necessary to calculate the electrode abrasion amounts, the advantageous effect is limited to a single robot. In a spot welding step, a plurality of robots often work to process a single workpiece, and it is necessary to manage the working time of each robot. For example, when a plurality of robots execute different kinds of electrode inspections, some of the robots that execute a short-time electrode inspection need to be on standby since they cannot proceed to the next step until the other robots complete electrode inspection, which may cause reduction of overall work efficiency. In addition, in the technique of JP-A-2000-176649, accurate detection of electrode abrasion amounts cannot be executed during cycle operation, so that accuracy of the positioning of the electrode can be reduced.
Thus, there has been a need for a spot welding system capable of efficiently managing electrode inspections executed in a plurality of robots.